Control method and means for obtaining optimum yields of refined oil and extract oil from charge oil

ABSTRACT

A system and method for controlling the solvent refining of a charge oil to obtain refined waxy oil of a specific quality which is subsequently dewaxed to provide refined oil. During a predetermined time period, the characteristics of the charge oil are sensed and corresponding signals provided. After the predetermined time period, characteristics of the charge oil, the refined waxy oil, extract oil and solvent are sensed and corresponding signals provided. Analog computers provide signals in accordance with equations, hereinafter disclosed, for controlling the charge oil flow rate and the temperature of the extract-mix in accordance with the condition signals and other signals corresponding to the current economic values of the charge oil, the refined oil and the extract oil.

United States Patent Woodle 1451 May. 30, 1972 [54] CONTROL METHOD ANDMEANS FOR 3,458,691 7/1969 Boyd, Jr ..23s/151.12 OBTAINING OPTIMUMYIELDS F 3,539,784 11/1970 Woodle ..23s/1s1.12

REFINED OIL AND EXTRACT OIL Primary Examiner-Eugene G. Botz FROM CHARGEOIL Attorney-Thomas 11. Whaley and Carl 0. Reis 72 Inventor: Robert AlanWoodle, Nederland, Tex. 1 [57] ABSTRACT 73 Assi nee: Texaco Inc. NewYork, NY. 1 g A system and method for controlling the solvent refiningof a [22] Filed: Dec. 8, 1970 charge oil to obtain refined waxy oil of aspecific quality which is subsequently dewaxed to provide refined oil.During a [2]] Appl 96193 predetermined timeperiod, thecharacteristics'of the charge oil are sensed and corresponding signalsprovided. After the 52 us. c1. ..23s/1s1.12, 208/DIG. 1, 208/311predetermined time Period, characteristics of the charse'oil, [51] Clog2 00 051, 15 02 the refined waxy oil, extract oil and solvent are sensedand [58] Field of Search ..235/151.12; 208/DIG. 1 corresponding Signalsprovided- Analog computers P d signals in accordance with equations,hereinafter disclosed, 56] References Cited for controlling the chargeoil flow rate and the temperature of the extract-mix in accordance withthe condition signals and UNITED STATES PATENTS other signalscorresponding to the current economic values of the charge oil, therefined oil and the extract oil. 1 3,285,846 11/1966 King et a1...208/DIG. l UX 3,458,432 7/1969 Woodle et a1. ..208/DIG. l UX 14Claims, Drawing Figures EB I 30 /El2 RE NEI RE FINING E TOWER f5 24SOLVENT DEWAX'NG 37 fif f T 48 WAX RE R ER 2/4 1 STRIPPER CONTROLLER 4 4C'B d ER E STRIPPER =5 |8 COOLING CHARGE 'V 8B OIL 5; WATER 5o EXTRACTOIL 1 48 E3 I Y 447 REQEJ A SER vd 1 17 1 no 3 i gg A FLOW 1r TARG. 30 1X91 RECOR DER FRED. .E, COMPUTER 5'5 1 'YQ CONTROLLER l8 5] -COMPUTER c-8 i 5 E E 0 ACT i "f Em En 5,, 32 (66 com ren V 's 9 1- q E PRED. 4I x11 E 55 E1 coM PUTER sw. P 34 Q; E11* 100 E COMPUTER 460 21o Ev 185 -E Ev 38 38 E COMPUTER Cd E24 W E \lae L. T MAX? L 1 L FRED L E44 COMPUTER'f- E EC COMPUTE R Y V E9 64 v W MAX. P

' E: h I61 E COMPUTER Patented May 30, 1972 4 Sheets-Sheet l PatemitedMay 30, 1972 3,666,931

4 Sheets-Sheet 5 E FIG.5 E

EXPONENTIAL DIVIDER CRCUT MULTIPLIER [I06 V ('07 :Egg MULTIPLIER 4 E I27 Q I I T u PRED. COMPUTER I u 7 EV 'f V0 C6 FIG. 6 l E E E S 52EXPONENTIAL 3 T CIRCUT DIVIDER i MULTIPLIER l5| 122 23 I 1 I I DIVIDEREXPONENTIAL CIRCUIT 0 ACT. COMPUTER T I29 L J V e E4 S 34 MULTIPLIERMULTIPLIER DIVIDER l L k :38 m2 l :4? l ('46 I g l EXPONENTIAL CIRCUTMIVULTIPLIVEYR "Isl T I EXPONENTIAL CIRCUIT A ACT. I r

I l "fi l Patented May 30, 1972 3,666,931

4' Sheets-Sheet 4 60 V L Vn I E |67 TIE I'T5 't i 4 MULTI- MULTI- EXPON-I EXPON- PLIER PUER DIVIDER ENTIAL ENTIAL l I CIRCUIT I cIRcuI'r I76 I80I I72 38 I I I l :lal DIVIDER l x MAX. P I :YMAXP I E EE L E I IE E L EEl -1 E I l E, 0, MAX. P COMPUTER 202 IEIZ l8 EXPON- I ..0IvI0ER ENTIAL'g i'fg DIVIDER l CIRCUIT [I87 M90 l89 200 T I I MULTI- MULTIPLIER PUERf l 1 EXPON- l l |9| l94 EN'HAL I CIRCUIT I I l I I l l l VF s v1 E40E38 u I ENPONENTIAL CIRCUIT r I I FEED I l BA K I I LOG AMP CIR IT a I EI I MULTIPLIER l l 205 OPERATIONAL AME:

CONTROL METHOD AND MEANS FOR OBTAINING OPTIMUM YIELDS OF REFINED OIL ANDEXTRACT OIL FROM CHARGE OIL I BACKGROUND OF THE INVENTION 1. Field ofthe Invention The device of the present invention relates to controlsystems and, more particularly, to an automatic control system for usein an oil refinery.

2. Description of the Prior Art Heretofore, a control system for asolvent refining unit, such as disclosed in US. Pat. No. 3,458,432, isable to provide refined oil of a quality determined by the viscosityindex (VI) of the refined oil. However, the VI of the refined oil,although important, is only one of several quality factors which need tobe established before the refined oil can be converted to a commerciallyvaluable product. For example, in inhibited heavy duty motor oil, otherimportant quality factors are: sulfur content, susceptibility toreduction of pour point by pour depressant additives, and susceptibilityto inhibition by engine cleanliness additives, and susceptibility toinhibition by engine cleanliness additives and corrosion and oxidationinhibitors. The means and method of the present invention utilizes therefractive index of the refined waxy oil as yet another characteristicto define the quality of the refined oil.

The means and method of the present invention further differs from US.Pat. No. 3,458,432 by using certain characteristics of the charge oil incontrolling the flow rate of the charge oil and the temperature of theextract oil for a predetermined time period and thereafter using therefractive indices of the charge, oil and the refined waxy oil and theflow rates of the solvent, the refined waxy oil and the extract oil incontrolling the flow rate of the charge oil and the temperature of theextract-mix.

The means and method of the present invention further distinguishes overthe aforementioned US. patent in controlling the flow rate of the chargeoil and the temperature of the extract-mix in accordance with thecurrent economic values of the crude oil, the extract oil and therefined oil so as to provide optimum yields of the refined oil ant. theextract oil.

SUMMARY OF THE INVENTION A system for controlling the refining of chargeoil to obtain optimum yields of refined oil and extract oil where in therefining operation the charge oil is treated with a solvent in arefining tower and a stream of raffinate and'a stream of extract-mix arewithdrawn from saidv tower, strippers separate the solvent from theraffinate and from the extract-mix to provide refined waxy oil and theextract oil, respectively. The refined waxy oil is subsequently dewaxedto yield the refined oil. The control system includes sensing circuitswhich sense the characteristics of the charge oil, the refined waxy oil,the extract oil, and the solvent and provide corresponding conditionsignals. A signal source provides signals that correspond to theeconomic values of the charge oil, the extract oil, and the refined oil.Control circuits control some of the conditions of the refined waxy oiland the extract oil in accordance with the condition signals and thevalue signals from the sensing circuits and the signal source,respectively, to provide the optimum yields of the refined oil and theextract oil.

One object of the present invention is to control quantities of refinedoil and extract oil and the temperature of the extract-mix duringrefining of crude oil so as to obtain optimum yields of the refined oiland the extract oil.

Another object of the present invention is to control the flow rate ofcharge oil and the temperature of extract-mix during the refining of thecharge oil in accordance with predicted values, determined from sensedconditions of the charge oil, for a predetermined time period and afterthe predetermined time period in accordance with sensed conditions of asolvent, refined waxy oil and extract oil.

Another object of the present invention is to control the refining ofcharge oil in accordance with the economic values of the charge oil,extract oil and refined oil.

Another object of the present invention is to control the refining ofcharge oil to provide refined oil of a quality characterized by apredetermined viscosity index and a predetermined refractive index.

Another object of the present invention is to provide an automaticcontrol system for use in the solvent refining of charge oil to provideoptimum yields of extract oil and refined oil which considers thedesired quality of the refined oil, the refining conditions, and theeconomic values of the charge oil, the extract oil and the refined oil.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingswherein one embodiment of the invention is illustrated by way ofexample. It is to be expressly understood, however, that the drawingsare for illustration purposes only and are not to be construed asdefining the limits of the invention. i

DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified block diagram of asystem for refining charge oil using an automatic control system,constructed in accordance with the present invention, to obtain optimumquantities of refined oil and extract oil from the charge oil.

FIGS. 2 through 9 are detailed block diagrams of the H computer, Acomputer, the 5.0 computer, the a computer, the a computer, the acomputer, the A computer, the X computer, the Y computer, and the Tcomputer blocks shown in FIG. 1.

FIG. 10 is a block diagram of an exponential circuit of the type whichmay be used in the a,,,,,,, computer, the a computer, the a computer,the A computer, the X computer, the Y computer and the T computer shownin FIGS. 5 through 9.

, DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown acontrol system for a conventional type furfural refining operation forproviding an optimum yield of refined oil. The rate of flow of thecharge oil is controlled so as to control the flow rates of refined waxyoil and extract oil. The temperature, which is also controlled, at whichthe refining of the charge oil takes place also affects the yield of therefined waxy oil and the extract oil. The rate of the charge oilentering a furfural refining tower 5 in a line 6 is sensed andcontrolled by conventional types sensing element 8, flow recordercontroller 10 and valve 14. Sensing element 8 provides a signal tocontroller 10 corresponding to the flow rate of charge oil. Controller10 operates valve 14 to control the rate of flow of the charge oil totower 5 in accordance with the signal from sensing element 8 and asignal E,. Signal E, controls the set points of controller 10.

The charge oil is also sampled by a refractive index meter 17, a flashmeter 18, a viscosity meter 19, a gravity meter 20 and the effluent fromthose meters may be applied to tower 5 or disposed of as slop.Refractive index meter 17, which may be of the type described by G. C.Eltenton in US Pat. No. 2,569,127, provides a signal E corresponding tothe refractive index of the charge oil. Flash meter 18 provides a signalE corresponding to the Cleveland Open Cup Flash Point of the charge oil.A suitable meter for this purpose is the Precision Scientific AutomaticFlash Tester recalibrated for the Cleveland Open Cup Flash Point.Viscosity meter 19 provides a Although not shown, for ease ofexplanation, the charge oil and a furfural refining solvent enteringtower 5 through lines 6 and 24, respectively, have been heated to apredetermined temperature. Tower 5 contains packing 26 where the chargeoil and solvent are contacted in counter current flow efiecting theextraction of low viscosity index constituents of the charge oil.Rafi'inate including the refined waxy oil and a small amount ofdissolved solvent is withdrawn through line 30.

A temperature gradient is maintained in tower 5 by means of a coolingoil 32 having cooling water flowing through it. The temperature in tower5 is sensed by conventional type sensing means 34 which provides acorresponding signal to a temperature recorder controller 37.Temperature recorder controller 37, which may be of a type wellknown inthe art, operates a valve 38 in accordance with the signal fromtemperature sensing means 34 and a signal E Signal E controls the setpoints of temperature recorder controller 37. Valve 38 controls the rateof flow of the cooling water to control the temperature in tower 5.Temperature controller recorder 37 also provides asignal E whichcorresponds to the temperature T of the extract-mix.

Raffinate'in line 30 enters a stripper 40 which strips the solvent fromthe raffinate to yield the refined ,waxy oil. The solvent aftertreatment for the removal of water-in any suitable manner (e.g.Hydrocarbon Processing, Sept. 1966, Volume 45, Number 9, page 226) isreturned to tower 5 by line 24 while the refined waxy oil is provided todewaxing element 39 through a line 41. Element 40 removes the wax andprovides refined oil for storage and blending with product lubricatingoil. The refined waxy oil in line 41 is continuously sampled by arefractive index meter 17A, which providesa corresponding signal E andthe effluent is either-returned to line 41 or disposed of as slop.Elements having a numerical designation with a suffix are identical inoperation and connection to elements having the same numericaldesignation without a suffix.

Sensing means 8A and a conventional type flow recorder 44 measures therate of flow of the refined waxy oil from stripper 40 and provides acorrespondingsignal E,

Extract-mix comprising solvent and dissolved low viscosity indexconstituents of the charge oil is withdrawn from tower 5 through line 48at a temperature controlled by cooling coil 32. The extract-mix in line48 is passed to.a stripper 49 where the solvent is stripped from theextract oil which is discharged through a line 50. The recovered solventis withdrawn through line 24 for return to tower 5 and r'e-use. Sensingmeans 88 and a flow recorder 44A senses the rate'of flow of extract oilin line 50 and provide a corresponding signal E Sensing means 8C and aflow recorder 44B'senses the flow rate of solvent in lirie 24 andprovides a corresponding signal E When starting the refining of newcharge oil, the characteristics of the extract oil and the refined waxyoil are initially unsettled due to the presence of old charge oil in thesystem. The control system of the present invention provides for thiscondition by controlling the quality of the refined waxy oil, usingpredictive values, for a predetermined time period of suitable durationto allow the characteristics of the refined waxy oil and the extract oilto stabilize. After the predetermined time period has elapsed, thecontrol system of the 7 present invention senses the conditions of therefined waxy oil and the flow rates of the extract oil and the refinedwaxy oil to control the process.

It has been found that the quality of the refined waxy oil can bepredicted to acertain extent by the following equations:

H= 870 Log Log (V,\.+ 0.6) 154 1, 94.9 0.149 H- 0.0826 Ala 0.0001 H2 2,

where H is the Bell and Sharpviscosity function of the charge oil at 210Fahrenheit, V is the kinematic viscosity of the charge oil at 210Fahrenheit, API is the API gravity-of the charge oil, A is the predictedcharacteristic constant for the charge oil, E0 is the predicted extractoil yield in percent by volume, R1, is the refractive index of thecharge oil, F! is the flash point of the crude oil, V1 is the desiredVI, a is the predicted characteristic constant for a desired quality ofrefined oil, S is the flow rate of the solvent in line 24 to tower 5,and constants C and C are constants having the following values:

Type of Charge Oil C, C,

Light Distillates 12.7 [.333 Heavy Distillates 25.4 1.668 Residual Oill7.3 1.373

Signal E corresponding to the kinematic viscosity V term in Equation 1,is applied to an H computer 55 which also receives direct currentvoltages E E, and E, and which provides a signal E corresponding to H inaccordance with Equation 1. Referring to FIG. 2, signal E, is summedwith voltage E,,, which corresponds to the term 0.6 in Equation 1, bysumming means 57. The resulting sum signal is amplified by conventionaltype logarithmic amplifiers 58, 58A to provide a signal, correspondingto the log log of the sum signal from summing means 57, to a multiplier60. Multiplier 60 multiplies the signal from logarithmic amplifier 58Awith voltage E corresponding to the coefficient 870 in Equation 1, 'toprovide a product signal. Summing means 61 sums the product signal frommultiplier 60 with voltage E which corresponds to the term 154 inEquation 1, to provide signal E Signal E is applied to an A computer 64,as'shown in FIG. 1, along with signal E, from gravity meter 20 anddirect current voltages E,,,, E E, and E,,. Computer 64 provides asignal E corresponding to 0.1.4,, of Equation 2. Referring to FIG. 3, amultiplier 66 in computer 64 multiplies signal E with voltage E whichcorresponds to the 0.149 coefficient in Equation 2, to provide a productsignal to subtracting means 67. Subtracting means subtracts the productsignal from multiplier 66 from voltage E,, which is related to the term94.9 in Equation 2, to provide a corresponding signal. Signal E iseffectively squared by a multiplier 70 and the resulting signal ismultiplied with voltag E, which corresponds to the 0.0001 coefl'lcientin Equation 2, by a multiplier 71. Gravity signal E, is effectivelysquared by a multiplier 73 and the resulting signal is multiplied withvoltage E,,, which corresponds to the coefficient 0.0826 in Equation 2,by a multiplier 74 to provide a corresponding product signal. Theproduct signal from multiplier 74 is subtracted from the product signalfrom multiplier 71 by subtracting means 77 to provide a signal tosumming means 78. Summing means 78 sums the signal from subtract- 7 ingmeans 67, 77 to provide signal E Referring again to FlG. 1, an 12.0computer 70-receives signals E E from refractive index meter 17 andflash-meter 18, respectively, and direct current voltages E, through E,,and uses the signals and voltages to provide a signal E corresponding tothe term BO in Equation 3. Referring to FIG. 4, signal E, fromrefractive index meter 17 is applied to subtracting means 80 whichsubtracts voltage E corresponding to the term 1.49 in Equation 3, fromsignal E The signal resulting from subtracting means 80 is multipliedwith voltage E. by a multiplier 81 and the resulting product signal isap-i plied to subtracting means 84. Signal E from flash meter 18 ismultiplied with voltage E,, which corresponds to the coefficient 0.1 inEquation 3, by a multiplier 85 and the resulting product signal isapplied to subtracting means 84. A multiplier 88 multiplies the outputfrom subtracting means 84 with voltwith voltage 15,, which is a variableamplitude voltage that corresponds to the constant C in Equation 3, toprovide a product signal to subtracting means 94. Subtracting means 94subtracts the product signal from multiplier 90 from the sum signal fromsumming means 93 to provide signal E A signal E is provided by an acomputer 100 in accordance with signals E E from flow recorder 44B andE.O.,,,,,, computer 70, respectively, direct current voltages E,, E,, Eand E,,, asshown in FIG. 1, and Equation 4. All terms and coefficientsreferred to in the following description of computer 100 occur inEquation 4. Referring to FIG. 5, signal E received by computer l-andcorresponding to the S term, is divided by voltage E,, which correspondsto the term 1,000, by a divider 101. The resulting signal is raised tothe power of 0.35 by an exponential circuit 102, which may be of thetype shown in FIG. 10, receiving voltage E, corresponding to theexponent 0.35. The output from circuit 102 is multiplied with voltage Ecorresponding to the coefficient 0.464, by a multiplier 106 to provide aproduct signal to another multiplier107. Signal E 21 from E.0.,,,.,,computer 70 is applied to a divider 108 where voltage E,,, whichcorresponds to the term 100, is divided by signal E Subtracting means112 subtracts voltage 15,, which corresponds to the term 1, from thesignal from divider 108 to provide a corresponding output. A multiplier107 multiplies the product signal from multiplier 106 with the outputfrom the subtracting means 112 to provide signal E Referring to FIG. 10,a typical exponential circuit receives a signal E corresponding to avalue A and a direct current voltage V corresponding to a value B andprovides a signal corresponding to A. The exponential circuit includes aconventional type logarithmic amplifier 205 which provides a signalcorresponding to the logarithm of signal E. A multiplier 208 multipliesthe signal from logarithmic amplifier 205 with the voltage to provide aproduct signal to a conventional type operational amplifier 210.Amplifier 210 has a feedback circuit 212, which may be of the typemanufactured by Pace under part number PC-l2, causing amplifier 210 toprovide the signal corresponding to A". All exponential circuitshereinafter referred to may be of the aforementioned type.

After the predetermined time period has elapsed, the quality of therefined oil is controlled by using monitored values obtained during therefining process in lieu of predicted values in accordance with thefollowing equations:

0.935 (X (323 TI-1.0.)

where a is the actual characteristic constant for the desired quality ofrefined oil, Y, is the flow rate of refined waxy oil in line 41, X isthe flow rate of extract oil in line 50m is the target characteristicconstant foi' a desired quality of refined oil, ARI is the actualdifference between the refractive index of the charge oil and therefractive index of the refined waxy oil, ARI is the target refractiveindex difference, S is the flow rate of the solvent in line 24 and T isthe temperature of the extract-mix.

Referring to FIGS. 1 and 6', an a computer 116 computes a in accordancewith signals E, E from flow recorders 44 and 44A, respectively, a directcurrent voltage V,,, and equation to provide a corresponding signal E toan A computer 1 l8. Signal E from flow recorder 44A, corresponding tothe X, term in Equation 5 and to the flow rate of the refined waxy oilin line 41, is raised by a power of 0.65 by an exponential circuit 122,which receives voltage V, corresponding to the exponent 0.65, and aresulting output is applied to a divider 123. Divider 123 divides signalE from recorder 44, corresponding to the Y term in Equation 5 and to theflow rate of the extract oil in line 50, by the resulting output fromexponential circuit 122 to provide signal E corresponding to the term ain equation 5.

Computer 118 provides a signal E corresponding to A in accordance withsignals E E and E from refractive index meters 17, 17A and A computer116, respectively, direct current voltages V V,. and Equation 6.Subtracting means 127 subtracts signal E provided by refractive indexmeter 17 from signal E from refractive index meter 17 to provide asignal corresponding to the ARI term in Equation 6. A direct currentvoltage V,,, which corresponds to the term ARI is applied to a divider128 which divides the signal from subtracting means 127 by voltage V,,,which corresponds to ARI in Equation 6, to provide a correspondingoutput. The output from divider 128 is effectively cubed by anexponential circuit 129, receiving voltage V, which corresponds to theexponent 3.0, to provide an output to a multiplier 130. Multiplier 130vmultiplies the output from exponential circuit 129 with signal E from Acomputer 116 to provide signal Referring to FIGS. 1 and 7, an A computer134 provides a signal E corresponding to the term 0.1.4,, in Equation 7in accordance with signals E E E and E from temperature recordercontroller 37, flow recorders 44, 44A and 443, respectively, directcurrent voltages V,,, V,., V, and V,,, and Equation 7. Subtracting means135 subtracts signal E corresponding to the temperature T of theextract-mix, from voltage V,,, which corresponds to the term 323 inEquation 7, to provide an output to a multiplier 137 where it ismultiplied with voltage V, which corresponds to the term 0.935. Anothermultiplier 138 multiplies the output from multiplier 137 with signal Ecorresponding to the flow rate X, of the extract oil in line 50, toprovide a product signal to a divider 142. Summing means sums signal Ewhich corresponds to the flow rate Y of the refined waxy oil in line 41,with signal E to provide an output to exponential circuit 146 whichreceives voltage V, corresponding to the exponent 0.5 in equa tion 5.Exponential circuit 146 provides a corresponding signal to a multiplier147. A divider 150 divides signal E which corresponds to the flow rate Sof the solvent in line 24, by voltage V, which corresponds to the term1,000 in Equation 7. An exponential circuit 151, which also receivesvoltage V,, raises the signal from divider 150 to the power of 0.5 andprovides a corresponding signal. The signals from exponential circuits146, and 151 are multiplied with each other by multiplier 147 to providea product signal. Divider 142 divides the product signal from multiplier138 with the product signal from multiplier 147 to provide signal E;,.,.

The quality of the refined oil is a constant for different sets ofvariable conditions. The flow rate of the charge oil and the temperatureof the extract-mix leaving tower 5 may be simultaneously varied withoutchanging the quality of the refined oil. The flow rate of the charge oiland the temperature of the extract-mix are controlled in accordance withthe following equations to provide optimum refining of the charge oil.

where A is the predicted characteristic constant A for the charge stockduring the predetermined time period and the actual characteristicconstant A during the remainder of the refining process, X is themaximum profit flow rate of the extract oil in line 50, b is the valueof the refined oil in dollars per barrel, e is the value of the chargeoil in dollars per barrel, d is the value of extract oil in dollars perbarrel, Y is the maximum profit flow rate of refined oil in line 41, 2is the maximum profit flow rate of charge oil in line 23, and TLQMMP isthe maximum profit temperature of the extract-mixfrom tower 5.

Referring to FIG. 1, the maximum profit flow rate of extract oil in line50 is determined by an X computer 160 which provides a correspondingsignal E to summing means 161. Summing means sums signal E with a signalE from a Y computer 162, which corresponds to the maximum profit flowrate of the refined waxy oil in line 41, to provide signal Ecorresponding to the maximum profit flow rate of the charge oil in line23, to flow recorder controller 10. Switch 166 which may be of a typemanufactured by Eagle Signal Co., Moline, Illinois, as model HPS Series,Cycl-I-ilex Reset Timer, passes signal E from A computer 100, as asignal E duringthe predetermined time to computer 160. Switch 66 thenpasses signal 5,, from A computer 118 as signal E thereafter to Xcomputer 160. Computer 160 provides signal E in accordance-with thepassed signal E from switch 166, direct current voltages V V V V, andV,,,, and Equation 8. All the terms referred to in the-followingdescription of X computer 160 are contained in Equation 8.

Referring to FIG. 8, signal E from switch 166 is applied to a multiplier167 where'it is multipliedwith voltage V corresponding to the term 0.65,to provide a product signal. Voltage V,, which corresponds to the terme, is subtracted from voltage V which corresponds to the term 17, bysumming means 170 to provide a corresponding signal. A multiplier 171multiplies the product signal from multiplier 167 with the signal fromsubtracting means 170 to provide-a product signal. Subtracting means 172subtracts voltage V which corresponds to the term d, from voltage V toprovide a signal to a .divider 175. Divider 175 divides the productsignal from multiplier 171 by the signal from subtracting means 172. Theresulting output from divider 175 is raised to the power l/0.35 by anexponential circuit 176 receiving voltage V,,,, which corresponds to theexponent l/0.35 to provide signal E fReferring to FIGS. 1 and 8,' Ycomputer 162 provides signal E in accordance with signals E E andEquation 9. Signal E which corresponds to the XM term in Equation '9,is. raised to the. power 065 by an exponential circuit 180 receiving adirect current voltage V,, which corresponds to'the exponent 0.65 inEquation 9. A divider 181 divides signal E which corresponds to the termA in Equation 9,'by the output from exponential circuit 181 to providesignal E Referring to FIG. 1, the maximum profit temperature T i, of theextract-mix leaving tower is computed by a T "up computer 185 whichprovides signal E to temperature recorder controller 37 to control thetemperature of the extract-mix. Signal E is provided by computer 185 inaccordance with signals E E E from flow recorder 44B, X computer 160 andY computer 162, respectively, a signal E 'from a switch 186, and directcurrent voltages V,,, V V,, V,, V, and V, and equation 11. Switch 186passes signal E relating to A from computer 64 as signal E during thepredetermined time period and then passes signal E which corresponds toAm, from computer 134 thereafter as signal E a Referring to FIG. 9,signal E corresponding to the term S in Equation 1 l, is divided byvoltage V, which corresponds to the term 1,000, by a divider 187 inTgmmup computer 185. A signal corresponding to the resulting output fromdivider 187 raised to the 0.5 power is provided to a multiplier 189 byan exponential circuit 190 receiving voltage V corresponding to theexponent 0.5 in Equation 10. A multiplier 191 divides signal E fromswitch 186 by voltage V,, which corresponds to the coefficient 0.1 inEquation 11. The resulting output of multiplier 191 is multiplied withvoltage V,,- which corresponds to the term 0.935, by a multiplier 194.Multiplier 189 multiplies the signal from circuit with the productsignal from multiplier 194 to provide another product signal. Summingmeans 196 sums signals E and E corresponding to the X and Y terms,respectively, to provide a sum signal. An exponential circuit 197,receiving voltage V which corresponds to the exponent 0.5 in Equation10, provides a signal relating to the sum signal from summing means 196raised to the 0.5 power. A multiplier 200 multiplies the product signalfrom multiplier 189 with the signal from exponential circuit 197 toprovide a product signal to a divider 201 where the product signal isdivided by signal E,,,. Subtracting means 202 subtracts the output fromdivider 201 from voltage V,, corresponding to the term 323 in Equationll to provide signal E I Although the device of the present inventionhasbeen disclosed as using analog computers, a digital computer such asan 1800 Process Control Computer manufactured by IBM may be used.

Signals E E E E,, E E E E, and E from refractive index meter 17, flashmeter 18, viscosity meter 19, gravity meter 20, temperature recordercontroller 37, refractive index meter 17A, flow recorders 44,44A and448, respectively, are converted to digital signals by conventional typeanalog-todigital converters. The digital computer is programmed toprovide control signals in accordance with Equations -l through 9. Thecontrol signals are then converted to analog signals E, and E byconventional type digital-to-analog converters. I

The device of the present invention as heretofore described controlsquantities of refined oil and extract oil and the temperature ofextract-mix during refining so as to obtain optimum yields of refinedoil and extract oil during furfural refining of charge oil. The flowrate of the charge oil and the temperature of the extract-mix areautomatically controlled during the. refining of the charge oil inaccordance with predicted values, determined from sensed conditions ofthe charge oil, for a predetermined time period and in accordance with asensed condition of the charge oil, solvent, refined waxy oil and theextract oil. The device of the present invention also controls therefining of the. charge oil in accordance with the economic values ofthe charge oil, the extract oil and the refined oil. The refined oil hasa quality that is characterized by a predetermined viscosity index and apredetermined refractive index.

I Iclaim: I

l. A system for controlling the refining of charge oil to obtain optimumyields of refined oil and extract oil where the charge oil is treatedwith a solvent in a refining tower to yield raffinate and extract-mix,strippers separate the solvent from the rafiinate and from theextract-mix to provide refined waxy oil and the extract oil,respectively, the refined waxy oil is subsequently dewaxed to providethe refined oil and the solvent is fed back to the refining tower,comprising means for sensing characteristics of the charge oil, therefined waxy oil, the extract oil and the solvent and providing signalscorresponding thereto; means for providing signals corresponding to theeconomic values of the charge oil, the refined oil and the extract oil,and means connected to the sensing means and to the value signal meansfor controlling some of the conditions of the refined waxy oil and theextract oil in accordance with the condition signals and the valuesignals to provide the optimum yields of the refined oil and the extractoil.

2. A system as described in claim 1 in which the sensed conditions arethe refractive index of the charge oil, the flow rate and the refractiveindex of the refined waxy oil, the flow rate of the extract oil, thetemperature of the extract-mix, and the flow rate of the solvent; andthe controlled conditions are the flow rates of the refined waxy oil andthe extract oil and the temperature of the extract mix.

3. A system as described in claim 2 in which the flow rates of therefined waxy oil and the extract oil are controlled by controlling theflow rate of the charge oil and the temperature of the extract-mix.

4. A system as described in claim 3 in which the control means includesfirst signal means for providing signals corresponding to a first actualcharacteristic 0. IA and a desired characteristic a of the refined oilin accordance with the following equations:

where X, is the flow rate of the extract oil, T is the temperature ofthe extract-mix, Y is the flow rate of the refined waxy oil, S is theflow rate of the solvent, a is a second actual characteristic of therefined waxy oil, ARI, is the difference between the refractive index ofthe charge oil and the refractive index of the refined waxy oil, and ARIis the desired difference between the refractive index of the charge oiland the refractive index of the refined oil.'

5. A system as described in claim 4 in which the control means includescontrol devices for controlling the flow rate of the charge oil and thetemperature of the extract-mix,-and means connected to the first signalmeans and to the control devices for providing control signals to thecontrol devices corresponding to the flow rate Z of the charge oil formaximum profit and the temperature 71 of the extract-mix for maximumprofit, so that the control devices control the flow rate of the chargeoil and the temperature of the extractmix in accordance with the signalsfrom the first signal means and the following equations: 7

1/0135 MuIP 9 YMMP and

(0.935) (0.1A) (511000)"- (Ximp MaaP) T 11.0.11? 323 XMHP where a is 05,, X is the maximum profitable flow rate of the extract oil, Y is themaximum profitable flow rate of the refined waxy oil, S is the flow rateof the solvent, 0.1A is 0.1/1 b is the economic value of the refinedoil, d is the economic value of the extract oil, and e is the economicvalue of the charge oil.

6, A system as described in claim 5 in which the sensing means includesa pair of refractive index meters, one refractive index meter sensingthe refractive index of the refined waxy oil and providing acorresponding signal while the other refractive index meter senses therefractive index of the charge oil and provides a signal correspondingthereto, means connected to the refractive index meters for providing asignal corresponding to the difference between the refractive indicesARI, of the charge oil and the refined waxy oil, means for sensing thetemperature T of the extract-mix and providing a corresponding signal,and means for sensing the flow rates X,,,,, Y, and S of the extract oil,the refined waxy oil and the solvent, respectively, and providingsignals corresponding thereto.

7. A system as described in claim 6 in which the first signal meansincludes a first analog computer receiving direct current voltagescorresponding to the numeric values 0.935, 323, 1,000 in the firstmentioned equation and connected to the flow rate sensing means andproviding the signal corresponding to 0.1.4,, in accordance with thefirst mentioned equation, the received direct current voltages and thesignals corresponding to the flow rates X and Y of the refined waxy oiland the extract oil, respectively, a second analog computer connected tothe flow rate sensing means and receiving a direct current voltagecorresponding to the exponent 0.65 in the second mentioned equation andproviding a signal corresponding to the tenn a in the second mentionedequation in accordance with the second mentioned equation, the signalsfrom the flow rate sensing means corresponding to the flow rates X, andY of the extract oil and-the refined waxy oil, respectively, and thereceived direct current voltage; and a third analog computer connectedto the second analog computer and to the difference means and receivingdirect current voltages corresponding to the ARI term and the exponent3.0 in the third mentioned equation and providing the signalcorresponding to a in accordance with the third mentioned equation, thesignal corresponding to a from the second analog computer, the signalcorresponding to ARI from the difference means, and the received directcurrent voltages.

8. A system as described in claim 7 in which control signal meansincludes a fourth analog computer connected to the third analog computerand receiving variable direct current voltages corresponding to theterms b, d and e and a fixed direct current voltage corresponding to theexponent l/0.35 0.35 and the 0.65 in the fourth mentioned equation andproviding a signal corresponding to the maximum profit flow rate X ofthe extract oil in accordance with the fourth mentioned equation, thereceived direct current voltages and the signal from the third analogcomputer corresponding to the tenn a in the third mentioned equation andwhich also corresponds to the term a in the fourth and fifth mentionedequations; a fifth analog computer connected to the third and fourthanalog computers and receiving a direct current volt-' age correspondingto the exponent 0.65 in the fifth mentioned equation and providing asignal corresponding to the maximum profit flow rate of refined waxy oilY in accordance with the fifth mentioned equation, the signals from thethird and fourth analog computers and the received direct voltage;summing means connected to the fourth and fifth analog computers forsumming the signals from the fourth and the fifth analog computers toprovide the control signal to the control devices corresponding to Z forcontrolling the flow rate of the charge oil; and a sixth analog computerconnected to the first, fourth and fifth analog computers, to the flowrate signal means and receiving direct current voltages corresponding tothe terms 323, 0.935, and 0,5, in the seventh mentioned equation andproviding the control signal to the control devices corresponding toTBOMMP for controlling the temperature of the extract-mix in accordancewith the signals from the first, fourth and fifth analog computers, thesignal from the flow rate sensing means corresponding to the flow rateof the solvent, the received direct current voltages and the seventhmentioned equation.

9. A system of the kind described in claim 8 in which the sensing meansfurther comprises means for sensing the flash point Fl of the crude oil,and providing a corresponding signal; means for sensing the API gravityof the charge oil and providing a signal corresponding thereto, andmeans for sensing the kinematic viscosity V,, and providing acorresponding signal; and the control means further includes secondsignal means, connected to the kinematic viscosity sensing means, to theAPI gravity sensing means, to the other refractive index meter, to theflash point sensing means and to the flow rate sensing means forproviding signals corresponding to predicted first and secondcharacteristics of the refined waxy oil in accordance with the signalsfrom the kinematic viscosity sensing means, from the API gravity sensingmeans, from the other refractive index meter, from the flash pointsensing means and from the flow rate sensing means and with thefollowing equations:

H= 870 log log(V +O.6)+ 154, 01A 94.9.- 0.149 H 0.0826(API) 0,0001 1')"'l-j.(). 0.1281 [1,000 (RA -1.42) 0. l(F!)]-C,( 100 I VITI"U| where H isthe Bell and Sharp viscosity function of the. charge oil at 210 F., V isthe sensed kinematic viscosity of the charge oil at 210 F., APlisthesensed APlgravity of the charge oil, A is a predicted firstcharacteristic of the refined waxy oil, E .0. is the yield of extractoil in per cent by volume of charge oil, C is a constant of the chargeoil and equals 12.7 for light distillates, 25.4 for heavy distillatesand 17.3 for residual oil, R1, 1 charge oil, F1 is the sensed flashpoint of the charge oil, C, is another constant of the charge oil andequals 1.333 for light distillates, 1.668 for heavy distillates and1.373 for residual oil, W is the target viscosity index of the refinedoil, a is asecond predicted characteristic of the refined waxy oil, andS is the sensed fiow rate of the solvent; and switching means connectedto the first and second signal means and to the control signal means forpassing the signals from the second signal means to the'control signalmeans-during a predetermined timeperiod while blocking the signalsfromthe first signal means, and passing the signals from the firstsignal means to the control signal means while blocking the signals fromthe urn! l 0.215

second signal means afterthe predetennined time period, and

where the term a in the equations controlling the development of thecontrol signals corresponds to during the predetermined time period anda thereafter and theterm 0.1A in the equations controlling thedevelopment of the control signals corresponds to 0.114,, during thepredetermined time period and 01A,, thereafter.

10. -A system-as described in claim 9 in which the second signalmeansincludes a seventh analog computer connected to the kinematic viscositysensing means and receiving direct current voltages corresponding to theterms 870, 0.6 and 154 in the eighth mentioned equation and providing asignal corresponding to the Bell and Sharpe viscosity function]! inaccordance with the signal from the kinematic viscosity sensing means,the received direct current voltages, and the eighth mentioned equation;an eighth analog computer connected to the seventh computer, to the APIgravity sensing means and to the switching means and receiving directcurrent voltages corresponding to the terms 94.9, 0.149, 0.0826 and0.0001 in the ninth mentioned equation for providing a signal to theswitching means corresponding to 0. 1A,, in accordance with the signal,from the seventh computer, the signal from the APl gravity sensing meansand the received direct current voltages; and a ninth computer connectedto the flash point sensing means and to the other refractive index meterand receiving direct current voltages corresponding to the C 0.1281,1,000, 1.42, 0.1, C 100 terms in the tenth mentioned equation andproviding a signal corresponding to percent by volume E. 0. of extractoil obtained from the charge oil in accordance with signals from theflash point sensing means and the other refractive indexmeter, and thereceived direct current voltages; and a tenth comptiter connected to theflow rate sensing means, to the switching means and to the ninthcomputer and receiving direct current voltages corresponding to theterms 0.464, 1,000, 100 and l and the exponent 0.35 in the eleventhmentioned equation and providing the signal to the switching meanscorresponding to the second predicted characteristic a of the refinedoil in accordance with the signal from the ninth analog computer, a'signal from the fiow rate sensing means corresponding to the flow rate Sof the solvent and the received direct currentvoltages.

11. A method for controlling a refinery operation wherein charge oil ismixed with solvent in a refining tower to provide a stream of raffinateand a stream of extract-mix to strippers is the sensed refractive indexof the which strip the solvent from the raffinate and the extract-mix toyield refined waxy oil and extract oil, the stripped solvent is returnedto the refining tower and the refined waxy oil is subsequently dewaxedto provide refined oil; which comprises sensing conditions of therefined waxy oil, the extract oil and the solvent; providing signalscorresponding to the sensed conditions; providing signals correspondingto the economic values of the charge oil, the refined oil and theextract oil; and controlling some of the conditions of the refined waxyoil, the extract oil and the extract-mix in accordance with thecondition signals and the value signals.

12. A method as described in claim 11 in which the sensed conditions arethe refractive index of the charge oil, the flow rate and the refractiveindex of the refined waxy oil, the fiow rate of the extract oil, thetemperature of the extract-mix and the flow rate of the solvent; thecontrolled conditions are the flow rates'of the refined waxy oil and theextract oil; and the condition signals 0.1.4,, and a correspond to thesensed conditions in accordance with the following equations:

and

ARI Targ nd A R 11am) where 0.114 is one characteristic of the refinedwaxy oil, X is the flow rate of the extract oil, T is the temperature ofthe extract oil, Y is the flow rate of the refined waxy oil, S is theHow rate of the solvent, a is the other characteristic of the refinedwaxy oil, ARI is the difference between the refra'c- 1 tive index of thecharge oil and the refractive index of the refined waxy oil, and ARI isthe target difference between the refractive index of the chargeoil andthe'refractive index [a(0.65) (b il MaIP 9 I e-d YMQIP =m,

Z MaIP Ma1-P MruPn and ea/warp 323 XMGIP where X up is the maximumprofit flow rate of the extract oil, a is a b is the economic value ofthe refined oil, d is the economic value of the extract oil, e is theeconomic value of the charge oil, m is the maximum profit flow rate ofthe refined waxy oil, TEDMMP is the maximum profit temperature of theextract oil, 0.1A is 0.114,, and S is the How rate of the solvent;

14. A methodas described in claim 13 in which other sensed conditionsare the flash point, the API gravity and the kinematic viscosity of thecharge oil, and the condition signals further are signals 0.114,, and acorresponding to the sensed conditions in accordance with the followingequations:

01A 94.9 0.149 H- 0.0826 (API) 0.0001 H (EO' I),

12.7 when the charge oil is a light distillate, 25.4 when the charge oilis a heavy distillate and 17.3 when the charge oil is residual oil, R1,is the sensed refractive index of the charge oil, F1 is the sensed flashpoint of the charge oil, C is another constant of the charge oil andequals 1.333 when the charge oil is a light distillate, 1.668 when thecharge oil is a heavy distillate and 1.373 for residual oil, V1 is thetarget viscosity index of the refined oil, a is another constant of therefined waxy oil, and S is the sensed flow rate of the solvent; thecontrol signals Z and TLQMGM are provided in accordance with the 0.1.4,,and the a condition signals during a predetermined time period and withthe 0.1.4,, and the a condition signals thereafter, the term a in the,fourth and fifth mentioned equations corresponds to the 0 term of the Ilth mentioned equation during the predetermined time period and to theterm o in the third mentioned equation thereafter; and the term 0.1.4 inthe seventh mentioned equation corresponds to the term 0.114,, in theninth mentioned equation during the predetermined time period and to theterm 0.121,, in the first mentioned equation thereafter.

* I I l 39 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent:No. 3,666,931 Dated MAY 3 97 ROBERT A. WOODLE Inventor(s) It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

T- c [100 v1 1-, c 1 lin 68 I 6 2 TARG a. o umn 3, es and 9, should dlOO- rea. C VI a gat Column 5, line 48, should act act read a --(X I )O5 H act c (10 VI ARG at Column 11, line 6, should read 100- C VI Signedand sealed this 9th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A system for controlling the refining of charge oil to obtain optimumyields of refined oil and extract oil where the charge oil is treatedwith a solvent in a refining tower to yield raffinate and extract-mix,strippers separate the solvent from the raffinate and from theextract-mix to provide refined waxy oil and the extract oil,respectively, the refined waxy oil is subsequently dewaxed to providethe refined oil and the solvent is fed back to the refining tower,comprising means for sensing characteristics of the charge oil, therefined waxy oil, the extract oil and the solvent and providing signalscorresponding thereto; means for providing signals corresponding to theeconomic values of the charge oil, the refined oil and the extract oil,and means connected to the sensing means and to the value signal meansfor controlling some of the conditions of the refined waxy oil and theextract oil in accordance with the condition signals and the valuesignals to provide the optimum yields of the refined oil and the extractoil.
 2. A system as described in claim 1 in which the sensed conditionsare the refractive index of the charge oil, the flow rate and therefractive index of the refined waxy oil, the flow rate of the extractoil, the temperature of the extract-mix, and the flow rate of thesolvent; and the controlled conditions are the flow rates of the refinedwaxy oil and the extract oil and the temperature of the extract mix. 3.A system as described in claim 2 in which the flow rates of the refinedwaxy oil and the extract oil are controlled by controlling the flow rateof the charge oil and the temperature of the extract-mix.
 4. A system asdescribed in claim 3 in which the control means includes first signalmeans for providing signals corresponding to a first actualcharacteristic 0.1Aact and a desired characteristic aTarg of the refinedoil in accordance with the following equations:
 5. A system as describedin claim 4 in which the control means includes control devices forcontrolling the flow rate of the charge oil and the temperature of theextract-mix, and means connected to the first signal means and to thecontrol devices for providing control signals to the control devicescorresponding to the flow rate ZMaxP of the charge oil for maximumprofit and the temperature TE.O.MaxP of the extract-mix for maximumprofit, so that the control devices control the flow rate of the chargeoil and the temperature of the extract-mix in accordance with thesignals from the first signal means and the following equations:
 6. Asystem as described in claim 5 in which the sensing means includes apair of refractive index meters, one refractive index meter sensing therefractive index of the refined waxy oil and providing a correspondingsignal while the other refractive index meter senses the refractiveindex of the charge oil and provides a signal corresponding thereto,means connected to the refractive index meters for providing a signalcorresponding to the difference between the refractive indices DeltaRIact of the charge oil and the refined waxy oil, means for sensing thetemperature TE.O. of the extract-mix and providing a correspondingsignal, and means for sensing the flow rates Xact, Yact and S of theextract oil, the refined waxy oil and the solvent, respectively, andproviding signals corresponding thereto.
 7. A system as described inclaim 6 in which the first signal means includes a first analog computerreceiving direct current voltages corresponding to the numeric values0.935, 323, 1,000 in the first mentioned equation and connected to theflow rate sensing means and providing the signal corresponding to0.1Aact in accordance with the first mentioned equation, the receiveddirect current voltages and the signals corresponding to the flow ratesXact and Yact of the refined waxy oil and the extract oil, respectively,a second analog computer connected to the flow rate sensing means andreceiving a direct current voltage corresponding to the exponent 0.65 inthe second mentioned equation and providing a signal corresponding tothe term aact in the second mentioned equation in accordance with thesecond mentioned equation, the signals from the flow rate sensing meanscorresponding to the flow rates Xact and Yact of the extract oil and therefined waxy oil, respectively, and the received direct current voltage;and a third analog computer connected to the second analog computer andto the difference means and receiving direct current voltagescorresponding to the Delta RITarg term and the exponent 3.0 in the thirdmentioned equation and providing the signal corresponding to aTarg inaccordance with the third mentioned equation, the signal correspondingto aact from the second analog computer, the signal corresponding toDelta RIact from the difference means, and the received direct currentvoltages.
 8. A system as described in claim 7 in which control signalmeans includes a fourth analog computer connected to the third analogcomputer and receiving variable direct current voltages corresponding tothe terms b, d and e and a fixed direct current voltage corresponding tothe exponent 1/0.35 0.35 and the 0.65 in the fourth mentioned equationand providing a signal corresponding to the maximum profit flow rateXMaxP of the extract oil in accordance with the fourth mentionedequation, the received direct current voltages and the signal from thethird analog computer corresponding to the term aTarg in the thirdmentioned equation and which also corresponds to the term a in thefourth and fifth mentioned equations; a fifth analog computer connectedto the third and fourth analog computers and receiving a direct currentvoltage corresponding to the exponent 0.65 in the fifth mentionedequation and providing a signal corresponding to the maximum profit flowrate of refined waxy oil YMaxP in accordance with the fifth mentionedequation, the signals from the third and fourth analog computers and thereceived direct voltage; summing means connected to the fourth and fifthanalog computers for summing the signals from the fourth and the fifthanalog computers to provide the control signal to the control devicescorresponding to ZMaxP for controlling the flow rate of the charge oil;and a sixth analog computer connected to the first, fourth and fifthanalog computers, to the flow rate signal means and receiving directcurrent voltages corresponding to the terms 323, 0.935, and 0.5, in theseventh mentioned equation and providing the control signal to thecontrol devices corresponding to TE.O.MaxP for controlling thetemperature of the extract-mix in accordance with the signals from thefirst, fourth and fifth analog computers, the signal from the flow ratesensing means corresponding to the flow rate of the solvent, thereceived direct current voltages and the seventh mentioned equation. 9.A system of the kind described in claim 8 in which the sensing meansfurther comprises means for sensing the flash point Fl of the crude oil,and providing a corresponding signal; means for sensing the API gravityof the charge oil and providiNg a signal corresponding thereto, andmeans for sensing the kinematic viscosity Vk and providing acorresponding signal; and the control means further includes secondsignal means, connected to the kinematic viscosity sensing means, to theAPI gravity sensing means, to the other refractive index meter, to theflash point sensing means and to the flow rate sensing means forproviding signals corresponding to predicted first and secondcharacteristics of the refined waxy oil in accordance with the signalsfrom the kinematic viscosity sensing means, from the API gravity sensingmeans, from the other refractive index meter, from the flash pointsensing means and from the flow rate sensing means and with thefollowing equations: H 870 log log (Vk + 0.6) + 154 , 0.1Apred 94.9 -0.149 H - 0.0826(API)2 + 0.0001 H2 , E.O. C1 + 0.1281 ( 1,000(RIwc-1.42) - 0.1(Fl))-C2(100 -VITarg), and where H is the Bell andSharp viscosity function of the charge oil at 210* F., Vk is the sensedkinematic viscosity of the charge oil at 210* F., API is the sensed APIgravity of the charge oil, Apred is a predicted first characteristic ofthe refined waxy oil, E.O. is the yield of extract oil in per cent byvolume of charge oil, C1 is a constant of the charge oil and equals 12.7for light distillates, 25.4 for heavy distillates and 17.3 for residualoil, RIwc is the sensed refractive index of the charge oil, Fl is thesensed flash point of the charge oil, C2 is another constant of thecharge oil and equals 1.333 for light distillates, 1.668 for heavydistillates and 1.373 for residual oil, VITarg is the target viscosityindex of the refined oil, apred is a second predicted characteristic ofthe refined waxy oil, and S is the sensed flow rate of the solvent; andswitching means connected to the first and second signal means and tothe control signal means for passing the signals from the second signalmeans to the control signal means during a predetermined time periodwhile blocking the signals from the first signal means, and passing thesignals from the first signal means to the control signal means whileblocking the signals from the second signal means after thepredetermined time period, and where the term a in the equationscontrolling the development of the control signals corresponds to apredduring the predetermined time period and aTarg thereafter and the term0.1A in the equations controlling the development of the control signalscorresponds to 0.1Apred during the predetermined time period and 0.1Aactthereafter.
 10. A system as described in claim 9 in which the secondsignal means includes a seventh analog computer connected to thekinematic viscosity sensing means and receiving direct current voltagescorresponding to the terms 870, 0.6 and 154 in the eighth mentionedequation and providing a signal corresponding to the Bell and Sharpeviscosity function H in accordance with the signal from the kinematicviscosity sensing means, the received direct current voltages, and theeighth mentioned equation; an eighth analog computer connected to theseventh computer, to the API gravity sensing means and to the switchingmeans and receiving direct current voltages corresponding to the terms94.9, 0.149, 0.0826 and 0.0001 in the ninth mentioned equation forproviding a signal to the switching means corresponding to 0.1Apred inaccordance with the signal from the seventh computer, the signal fromthe API gravity sensing means anD the received direct current voltages;and a ninth computer connected to the flash point sensing means and tothe other refractive index meter and receiving direct current voltagescorresponding to the C1, 0.1281, 1,000, 1.42, 0.1, C2, 100 terms in thetenth mentioned equation and providing a signal corresponding to percentby volume E.O. of extract oil obtained from the charge oil in accordancewith signals from the flash point sensing means and the other refractiveindex meter, and the received direct current voltages; and a tenthcomputer connected to the flow rate sensing means, to the switchingmeans and to the ninth computer and receiving direct current voltagescorresponding to the terms 0.464, 1,000, 100 and 1 and the exponent 0.35in the eleventh mentioned equation and providing the signal to theswitching means corresponding to the second predicted characteristicapred of the refined oil in accordance with the signal from the ninthanalog computer, a signal from the flow rate sensing means correspondingto the flow rate S of the solvent and the received direct currentvoltages.
 11. A method for controlling a refinery operation whereincharge oil is mixed with solvent in a refining tower to provide a streamof raffinate and a stream of extract-mix to strippers which strip thesolvent from the raffinate and the extract-mix to yield refined waxy oiland extract oil, the stripped solvent is returned to the refining towerand the refined waxy oil is subsequently dewaxed to provide refined oil;which comprises sensing conditions of the refined waxy oil, the extractoil and the solvent; providing signals corresponding to the sensedconditions; providing signals corresponding to the economic values ofthe charge oil, the refined oil and the extract oil; and controllingsome of the conditions of the refined waxy oil, the extract oil and theextract-mix in accordance with the condition signals and the valuesignals.
 12. A method as described in claim 11 in which the sensedconditions are the refractive index of the charge oil, the flow rate andthe refractive index of the refined waxy oil, the flow rate of theextract oil, the temperature of the extract-mix and the flow rate of thesolvent; the controlled conditions are the flow rates of the refinedwaxy oil and the extract oil; and the condition signals 0.1Aact andaTarg correspond to the sensed conditions in accordance with thefollowing equations:
 13. A method as described in claim 12 in which thecontrolling step includes providing control signals ZMaxP and TE.O.MaxPcorresponding to the maximum profit flow rate of the charge oil and tothe maximum profit temperature of the extract-mix, respectively, inaccordance with the 0.1Aact and the aTarg condition signals and thefollowing equations:
 14. A method as described in claim 13 in whichother sensed conditions are the flash point, the API gravity and thekinematic viscosity of the charge oil, and the condition signals furtherare signals 0.1Apred and apred corresponding to the sensed conditions inaccordance with the following equations: H 870 log log (Vk + 0.6) + 154,0.1Apred 94.9 - 0.149 H - 0.0826 (API)2 + 0.0001 H2 , E.O. C1 + 0.1281(1,000(RIwc-1.42) -0.1(Fl)) - C2(100- VITarg) , and where H is the Belland Sharp viscosity function of the charge oil at 210* F., Vk is thesensed kinematic viscosity of the charge oil at 210* F., API is thesensed API gravity of the charge oil, 0.1Apred is a predictedcharacteristic of the refined waxy oil, E.O. is the yield of extract oilin percent by volume of the charge oil, C1 is a constant of the chargeoil and equals 12.7 when the charge oil is a light distillate, 25.4 whenthe charge oil is a heavy distillate and 17.3 when the charge oil isresidual oil, RIwc is the sensed refractive index of the charge oil, Flis the sensed flash point of the charge oil, C2 is another constant ofthe charge oil and equals 1.333 when the charge oil is a lightdistillate, 1.668 when the charge oil is a heavy distillate and 1.373for residual oil, VITarg is the target viscosity index of the refinedoil, apred is another constant of the refined waxy oil, and S is thesensed flow rate of the solvent; the control signals ZMaxP and TE.O.MaxPare provided in accordance with the 0.1Apred and the apred conditionsignals during a predetermined time period and with the 0.1Aact and theaTarg condition signals thereafter, the term a in the fourth and fifthmentioned equations corresponds to the apred term of the 11th mentionedequation during the predetermined time period and to the term aTarg inthe third mentioned equation thereafter; and the term 0.1A in theseventh mentioned equation corresponds to the term 0.1Apred in the ninthmentioned equation during the predetermined time period and to the term0.1Aact in the first mentioned equation thereafter.